The present invention relates to an endoluminal stent for supporting a selected region of a body lumen and to a method of forming and delivering the stent in situ.
Atherosclerosis is commonly treated by means of angioplasty through the use of a balloon catheter. Balloon angioplasty involves passing a small, balloon-tipped catheter percutaneously into an artery or vessel and up to the region of obstruction. The balloon is then inflated to dilate the area of obstruction. However, restenosis or reclosure of the blood vessel following angioplasty is a common occurrence. Factors contributing, at least in part, to restenosis include proliferation of smooth muscle cells in the stenosed region and recoil of the arterial or vessel wall. When luminal narrowing occurs, further coronary difficulties can be experienced, including strokes, arrhythmia, infarcts and even death.
One approach to the prevention of restenosis following angioplasty has been to insert a supportive stent into the treated area. This can be done using a conventional balloon catheter. In particular, the stent is placed over the balloon portion of the catheter in a contracted or collapsed position. The catheter is then inserted into a blood vessel adjacent to a stenosis, and the balloon is expanded so that the stent engages and supports the surrounding vessel wall.
Typically, endovascular stents are made of metals to provide the requisite strength for maintaining dilation of a stenosed blood vessel region. For example, U.S. Pat. No. 5,197,978 (Hess et al.) and U.S. Pat. No. 5,354,308 (Simon et al.) disclose thermally deformable stents made of nickel and titanium. U.S. Pat. No. 5,366,504 (Andersen et al.) discloses a stent made of loosely interlocked knitted loops containing metal wire.
Non-metallic stents have also been used for endovascular support. These devices are generally cylindrical structures made up of a sheet or sleeve of resilient, elastic material which can be cured or hardened following delivery of the stent to a selected region of a vessel. For example, U.S. Pat. No. 5,100,429 (Sinofsky) discloses an endovascular stent having a tubular body formed as a rolled sheet of a biologically compatible material having a cross-linkable adhesive material between overlapping portions of the rolled sheet. U.S. Pat. No. 5,344,201 (Cowan et al.) discloses an endovascular stent made up of an expandable sleeve containing a cross-linkable material which can be cured by exposure to radiation, and a film of biologically compatible material which encapsulates the sleeve. U.S. Pat. No. 5,344,444 (Glastra et al.) discloses a hollow expandable stent in the form of a ring, cylinder or sleeve containing a curable material. U.S. Pat. No. 5,344,426 (Lau et al.) and U.S. Pat. No. 5,306,286 (Stack et al.) disclose stents made of a flat sheet of material which is rolled up to form a cylinder and having a plurality of apertures. U.S. Pat. No. 5,282,848 (Schmitt et al.) discloses a self-supporting stent having a continuous uniform surface made up of a woven synthetic material.
Many prior art stent designs suffer from the disadvantage of having a relatively large diameter in their non-deployed state, making them difficult to deliver and presenting the risk of causing undue trauma to the vessel Additionally, prior art stents can be somewhat inflexible so that they fail to closely conform to the surrounding vessel wall when in place. Moreover, these stents often become a permanent pan of the body and do not allow for significant tissue in-growth or exposure of the lumen wall to circulating blood when in place.
It is therefore an object of the present invention to provide a transformable stent for supporting and reinforcing a body lumen which is very flexible in its preformed state and tightly engages the surrounding lumen wall when expanded into place. It is also an object of the present invention to provide a stent which has a very low profile, so that it is easy to deliver and does not block a large portion of the lumen flow channel. It is a further object of the present invention to provide a stent which, following its delivery into a selected region of a body lumen, is extremely strong so as to effectively support and strengthen the surrounding lumen wall, yet which allows significant exposure of the supported lumen wall to circulating blood. It is still a further object of the invention to provide a polymer-based stent which is bio-resorbable and can be impregnated with a controlled release drug.